Cardiopulmonary resuscitation (CPR) is a well-known and valuable method of first aid used to resuscitate people who have suffered from cardiac arrest. CPR requires repetitive chest compressions to squeeze the heart and the thoracic cavity to pump blood through the body. Artificial respiration, such as mouth-to-mouth breathing or a bag mask apparatus, is used to supply air to the lungs. When a first aid provider performs manual chest compression effectively, blood flow in the body is about 25% to 30% of normal blood flow. However, even experienced paramedics cannot maintain adequate chest compressions for more than a few minutes. Hightower, et al., Decay In Quality Of Chest Compressions Over Time, 26 Ann. Emerg. Med. 300 (September 1995). Thus, CPR is not often successful at sustaining or reviving the patient. Nevertheless, if chest compressions could be adequately maintained, then cardiac arrest victims could be sustained for extended periods of time. Occasional reports of extended CPR efforts (45 to 90 minutes) have been reported, with the victims eventually being saved by coronary bypass surgery. See Tovar, et al., Successful Myocardial Revascularization and Neurologic Recovery, 22 Texas Heart J. 271 (1995).
Numerous studies establish that good quality chest compressions are difficult to accomplish from a psycho-motor skill level on the part of the rescuer as and also require up to 150 pounds of force to compress the sternum to a depth sufficient to accomplish adequate blood flow. As a result, rescuers frequently fatigue during CPR to the point that they cannot deliver adequate compressions.
In efforts to provide better blood flow and increase the effectiveness of bystander resuscitation efforts, various pneumatic or electrically powered mechanical devices (machine-powered devices) have been proposed for performing CPR. In one variation of these devices, a pneumatically driven piston is suspended over the patient using a rigid gantry, as in the LUCAS® CPR device, or suspended over the patient with a cantilevered gantry arrangement, as in the THUMPER® CPR device. The LUCAS® II device uses a motor driven piston. In these devices, the piston is forced repeatedly downward to push on the patient's chest and thereby compress the chest. In another variation of such devices, a belt is placed around the patient's chest and the belt is used to effect chest compressions. Our own patents, Mollenauer, et al., Resuscitation Device Having A Motor Driven Belt To Constrict/Compress The Chest, U.S. Pat. No. 6,142,962 (Nov. 7, 2000); Sherman, et al., CPR Assist Device with Pressure Bladder Feedback, U.S. Pat. No. 6,616,620 (Sep. 9, 2003); Sherman et al., Modular CPR assist device, U.S. Pat. No. 6,066,106 (May 23, 2000); and Sherman et al., Modular CPR assist device, U.S. Pat. No. 6,398,745 (Jun. 4, 2002), show chest compression devices that compress a patient's chest with a belt. Each of these patents is hereby incorporated by reference in their entirety. Our commercial device, sold under the trademark AUTOPULSE®, is described in some detail in our prior patents, including Jensen, Lightweight Electro-Mechanical Chest Compression Device, U.S. Pat. No. 7,347,832 (Mar. 25, 2008) and Quintana, et al., Methods and Devices for Attaching a Belt Cartridge to a Chest Compression Device, U.S. Pat. No. 7,354,407 (Apr. 8, 2008). U.S. Pat. No. 6,616,620 also described a system for controlling the compression wave-form of the device. The compression wave-form refers to the graph of FIG. 1, which plots the compression depth versus time for a chest compression. The graph illustrates the down-stroke phase of the compression stroke, during which the sternum is depressed from a relaxed state to a compressed state, a hold phase, during which the patient's sternum is held at a particular distance from the spine, a release phase during which the sternum is allow to recoil to its natural uncompressed condition, and an inter-compression phase during which the sternum is substantially released or held at some minimal threshold of compression.
Human powered CPR devices have been proposed, such as those described in Kelly, et al., Chest Compression Apparatus for Cardiac Arrest, U.S. Pat. No. 5,738,637 (Apr. 14, 1998). These human-powered devices typically use some form of mechanical advantage to minimize the amount of force required to compress the sternum and thus reduce rescuer fatigue. A weakness of these human powered systems is that they still rely on psychomotor skill set of the rescuer to deliver compressions with the proper waveform characteristics that result in optimal blood flow.